Turbidity in surface water

What is the turbidity?
Turbidity refers to the degree of obstruction of a solution to the passage of light, which includes the scattering of light by suspended matter and the absorption of light by solute molecules.
Turbidity is a parameter that describes the number of suspended particles in a liquid. It is related to factors such as the content, size, shape, and refractive index of suspended substances in the water. In water quality testing, turbidity is an important indicator, which can reflect the concentration of suspended solids in the water and is also one of the basis for people’s sensory evaluation of water quality. Turbidity is usually measured by measuring the amount of light scattered by particulate matter in the water when light passes through the water sample. These particulate matter are usually tiny, with sizes generally on the order of microns and below. The turbidity displayed by modern instruments is usually scattering turbidity, and the unit is NTU (Nephelometric Turbidity Units). The measurement of turbidity is very important for evaluating the quality of drinking water, because it is not only related to the clarity of the water, but also indirectly reflects the concentration level of microorganisms in the water, affecting the disinfection effect.
Turbidity is a relative measurement determined by how much light can pass through a water sample. The higher the turbidity, the less light will pass through the sample and the water will appear “cloudier”. Higher turbidity levels are caused by solid particles suspended in the water, which scatter light instead of transmitting it through the water. The physical properties of suspended particles may affect total turbidity. Larger sized particles scatter light and focus it forward, thereby increasing turbidity by interfering with the transmission of light through the water. Particle size also affects the quality of light; larger particles scatter longer wavelengths of light more easily than shorter wavelengths, while smaller particles have a greater scattering effect on shorter wavelengths. Increased particle concentration also reduces the transmittance of light as the light comes into contact with an increased number of particles and travels shorter distances between particles, resulting in multiple scatterings per particle.

Detection principle
Turbidity 90-degree scattering method is a commonly used method to measure the turbidity of solutions. This method is based on the scattering phenomenon described by the Lorentz-Boltzmann equation. This method uses a photometer or photometer to measure the intensity of light passing through the sample under test and the intensity of light scattered by the sample in the 90-degree scattering direction, and calculates the turbidity of the sample based on the measured values. The scattering theorem used in this method is: The Beer-Lambert Law. This theorem stipulates that under the action of a uniformly radiating plane wave, the electro-optical response within unit length decreases with the exponential function of the optical path length, which is the classic Beer-Lambert law. In other words, light rays hitting particles suspended in solution are scattered multiple times, with some rays being scattered at 90-degree angles. When using this method, the instrument will measure the ratio of the intensity of light scattered by these particles at a 90-degree angle to the intensity of light that passes through the sample without being scattered. As the concentration of turbidity particles increases, the intensity of scattered light will also increase, and the ratio is will be larger, therefore, the size of the ratio is proportional to the number of particles in the suspension.
In fact, when measuring, the light source is introduced vertically into the sample and the sample is placed at a position with a scattering angle of 90°. The turbidity value of the sample can be obtained by measuring the light intensity measured directly without passing through the sample and the 90° scattered light intensity generated in the sample with a photometer, and combined with the colorimetric calculation method.
This method has high accuracy and is widely used in turbidity measurement in water, wastewater, food, medicine and environmental fields.

What is the main cause of turbidity in surface water?
Turbidity in surface water is primarily caused by suspended matter in the water. 12
These suspended substances include silt, clay, organic matter, inorganic matter, floating matter and microorganisms, etc., which will prevent light from penetrating the water body, thus making the water body turbid. These particulate matter may originate from natural processes, such as storms, water scouring, wind blowing, etc., or from human activities, such as agricultural, industrial, and urban emissions. The measurement of turbidity is usually in a certain proportion to the content of suspended solids in the water. By measuring the intensity of scattered light, the concentration of suspended solids in the water can be roughly understood.
Measurement of turbidity
Lianhua turbidity meter LH-P305 uses the 90° scattered light method, with a measuring range of 0-2000NTU. The dual wavelengths can be automatically switched to avoid water chromaticity interference. The measurement is simple and the results are accurate. How to measure turbidity
1. Turn on the handheld turbidity meter LH-P305 to preheat, the unit is NTU.
2. Take 2 clean colorimetric tubes.
3. Take 10ml of distilled water and put it into the No. 1 colorimetric tube.
4. Take 10ml of sample and put it into colorimetric tube No. 2. Wipe the outer wall clean.
5. Open the colorimetric tank, put in the No. 1 colorimetric tube, press the 0 key, and the screen will display 0 NTU.
6. Take out the No. 1 colorimetric tube, put in the No. 2 colorimetric tube, press the measurement button, and the screen will display the result.
Application and summary
Turbidity is an important measure of water quality because it is the most visible indicator of how “clean” a water source is. High turbidity may indicate the presence of water contaminants that are harmful to human, animal and plant life, including bacteria, protozoa, nutrients (such as nitrates and phosphorus), pesticides, mercury, lead and other metals. Increased turbidity in surface water makes the water unsuitable for human consumption and may also provide waterborne pathogens such as disease-causing microorganisms to surfaces in the water. High turbidity can also be caused by wastewater from sewer systems, urban runoff, and soil erosion from development. Therefore, turbidity measurement should be widely used, especially in the field. Simple instruments can facilitate the supervision of water conditions by various units and jointly safeguard the long-term development of water resources.